<template>
  <ul class="list">
    <!--  touchstart : 触摸开始（手指放在触摸屏上）
          touchmove : 拖动（手指在触摸屏上移动）
          touchend : 触摸结束（手指从触摸屏上移开）  -->
    <li class="item" v-for="item of letters" :key="item" @click="handleLetterClick" @touchstart.prevent="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd" :ref="item">{{item}}</li>
  </ul>
</template>
<script>
  export default {
    props: {
      cities: {
        type: Object,
        default() {
          return {}
        }
      }
    },
    data() {
      return {
        touchStatus: false,
        startY: 0,
        timer: null
      }
    },
    updated() {
      this.startY = this.$refs['A'][0].offsetTop
    },
    computed: {
      letters() {
        const letters = []
        for(let i in this.cities) {
          letters.push(i)
        }
        return letters
      }
    },
    methods: {
      handleLetterClick(e) {
        /*console.log(e.target.innerText)*/
        this.$emit('change', e.target.innerText)
      },
      handleTouchStart() {
        this.touchStatus = true
      },
      handleTouchMove(e) {
        if(this.touchStatus) {
          if (this.timer) {
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
              const startY = this.startY
              const touchY = e.touches[0].clientY - 79
              const index = Math.floor((touchY - startY) / 20)
              if(index >= 0 && index < this.letters.length) {
                this.$emit('change', this.letters[index])
              }
            }, 16)
        }
      },
      handleTouchEnd() {
        this.touchStatus = false
      }
    }
  }
</script>

<style scoped lang="stylus">
  @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    align-items: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      color: $bgColor
</style>
